Bidirectional path edge data structure. More...

#include <mitsuba/bidir/edge.h>

Public Member Functions
Sampling-related functions
bool	sampleNext (const Scene scene, Sampler sampler, const PathVertex pred, const Ray &ray, PathVertex next, ETransportMode mode)
	Given a ray `ray`, sample a distance in this direction and fill the edge data structure, as well as its target vertex with content. More...

bool	perturbDirection (const Scene scene, const PathVertex pred, const Ray &ray, Float dist, PathVertex::EVertexType desiredType, PathVertex *next, ETransportMode mode)
	Create a perturbed successor vertex and edge. More...

Public Attributes
Enumerations and Fields
const Medium *	medium
	Pointer to the medium that contains this edge (where `NULL` is vacuum) More...

Vector	d
	Normalized direction vector associated with this edge. More...

Float	length
	Length of this edge in world-space distance units. More...

Spectrum	weight [ETransportModes]
	Measurement contribution weight. More...

Float	pdf [ETransportModes]
	Medium sampling density of the adjacent vertices. More...

Query functions
enum	ECachedValues { EValueImp = 0x01, EValueRad = 0x02, ECosineImp = 0x04, ECosineRad = 0x08, EValue = EValueImp \| EValueRad, ECosine = ECosineImp \| ECosineRad, EValueCosineImp = EValueImp \| ECosineImp, EValueCosineRad = EValueRad \| ECosineRad, EInverseSquareFalloff = 0x10, ETransmittance = 0x20, EGeometricTerm = ECosine \| EInverseSquareFalloff, EGeneralizedGeometricTerm = EGeometricTerm \| ETransmittance, EEverything = EValue \| EGeneralizedGeometricTerm }
	Evaluate cached quantities associated with this edge. More...

Spectrum	evalCached (const PathVertex pred, const PathVertex succ, unsigned int what) const
	Evaluate cached quantities associated with this edge. More...

Float	evalPdf (const PathVertex pred, const PathVertex succ) const
	Compute the density of a successor node. More...

Spectrum	evalTransmittance (const PathVertex pred, const PathVertex succ) const
	Compute the transmittance between an arbitrary pair of vertices. More...

Spectrum	evalTransmittance () const
	Return the transmittance value associated with this edge. More...

Float	evalCosine (const PathVertex pred, const PathVertex succ, const PathVertex *base) const
	Evaluate the one of the cosine factors associated with the geometric term over an edge. More...

Miscellaneous
bool	verify (const Scene scene, const PathVertex adjL, const PathVertex *adjE, ETransportMode mode, std::ostream &os) const
	Verify the cached values stored in this path vertex for consistency. More...

bool	connect (const Scene scene, const PathEdge predEdge, const PathVertex vs, const PathVertex vt, const PathEdge *succEdge)
	Create a connection edge between two vertices. More...

bool	pathConnectAndCollapse (const Scene scene, const PathEdge predEdge, const PathVertex vs, const PathVertex vt, const PathEdge *succEdge, int &interactions)
	Create a connection path between two vertices and collapse it into a single edge that summarizes its properties. More...

PathEdge *	clone (MemoryPool &pool) const
	Create a deep copy of this edge. More...

bool	operator== (const PathEdge &edge) const
	Compare this edge against another edge. More...

bool	operator!= (const PathEdge &edge) const
	Compare this edge against another edge. More...

std::string	toString () const
	Return a string representation of the information stored in this vertex. More...

static bool	pathConnect (const Scene scene, const PathEdge predEdge, const PathVertex vs, Path &result, const PathVertex vt, const PathEdge *succEdge, int maxInteractions, MemoryPool &pool)
	Create a connection path between two vertices. More...

Detailed Description

Bidirectional path edge data structure.

The path edge data structure is responsible for representing the transport of light between pairs of scattering or emission events. Amongst other things, it keeps track of the medium that fills the space between adjacent vertices of a Path. Furthermore, it can be used to evaluate and sample the visibility and transmittance functions of the scene.

Although they do not correspond to any real transport, this implementation also places edges next to "supernode" vertices (see PathVertex for a description), which simplifies the implementations of various rendering algorithms that make use of this framework.

See Also: PathVertex

Author: Wenzel Jakob

Member Enumeration Documentation

enum mitsuba::PathEdge::ECachedValues

Evaluate cached quantities associated with this edge.

This function computes the product of certain terms that are cached in this edge and its adjacent vertices. The what parameter specifies the terms to be included; it must be a combination of the flags in the enumeration ECachedValues.

Remarks: This function assumes that pred and succ are the vertices associated with this edge, and that they have not been modified since the edge was created.

Parameters

pred	The predecessor vertex of this edge
succ	The successor vertex of this edge

Enumerator
EValueImp
EValueRad
ECosineImp
ECosineRad
EValue
ECosine
EValueCosineImp
EValueCosineRad
EInverseSquareFalloff
ETransmittance
EGeometricTerm
EGeneralizedGeometricTerm
EEverything

Member Function Documentation

PathEdge* mitsuba::PathEdge::clone ( MemoryPool & pool ) const

Create a deep copy of this edge.

bool mitsuba::PathEdge::connect	(	const Scene *	scene,
		const PathEdge *	predEdge,
		const PathVertex *	vs,
		const PathVertex *	vt,
		const PathEdge *	succEdge
	)

Create a connection edge between two vertices.

This function can be used to create an edge data structure when connecting two separately sampled path vertices. This involves checking that they are mutually visible and computing the attenuation caused by the medium in between (if any).

Parameters

scene	Pointer to the underlying scene
predEdge	Pointer to an edge between `vs` and its predecessor (which is not needed by this function)
vs	First path vertex to be connected.
vt	Second path vertex to be connected.
succEdge	Pointer to an edge between `vt` and its successor (which is not needed by this function)

Returns: true upon success, false when there is no throughput or an inconsistency has been detected.

Spectrum mitsuba::PathEdge::evalCached	(	const PathVertex *	pred,
		const PathVertex *	succ,
		unsigned int	what
	)		const

Evaluate cached quantities associated with this edge.

This function computes the product of certain terms that are cached in this edge and its adjacent vertices. The what parameter specifies the terms to be included; it must be a combination of the flags in the enumeration ECachedValues.

Remarks: This function assumes that pred and succ are the vertices associated with this edge, and that they have not been modified since the edge was created.

Parameters

pred	The predecessor vertex of this edge
succ	The successor vertex of this edge

Float mitsuba::PathEdge::evalCosine	(	const PathVertex *	pred,
		const PathVertex *	succ,
		const PathVertex *	base
	)		const

Evaluate the one of the cosine factors associated with the geometric term over an edge.

Float mitsuba::PathEdge::evalPdf	(	const PathVertex *	pred,
		const PathVertex *	succ
	)		const

Compute the density of a successor node.

This function computes the hypothetical transport-related sampling density of a given successor node conditioned on a specified predecessor when using the sampling technique implemented by sampleNext(). Depending on whether or not the successor node is a medium interaction, the returned value is either a density per unit length or a discrete probability.

Note: this function only computes terms associated with the transport between vertices – to account for the vertices themselves, refer to PathEdge::evalPdf.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the preceding vertex
succ	Pointer to the successor vertex

Returns: The computed probability density

Spectrum mitsuba::PathEdge::evalTransmittance	(	const PathVertex *	pred,
		const PathVertex *	succ
	)		const

Compute the transmittance between an arbitrary pair of vertices.

This function queries the medium associated with this edge for the transmittance between an arbitrary pair of nodes, pred and succ.

Parameters

pred	Pointer to the preceding vertex
succ	Pointer to the successor vertex

Returns: A spectrally varying transmittance value

Spectrum mitsuba::PathEdge::evalTransmittance ( ) const

Return the transmittance value associated with this edge.

Parameters

pred	Pointer to the preceding vertex
succ	Pointer to the successor vertex

Returns: A spectrally varying transmittance value

bool mitsuba::PathEdge::operator!= ( const PathEdge & edge ) const

inline

Compare this edge against another edge.

bool mitsuba::PathEdge::operator== ( const PathEdge & edge ) const

Compare this edge against another edge.

static bool mitsuba::PathEdge::pathConnect	(	const Scene *	scene,
		const PathEdge *	predEdge,
		const PathVertex *	vs,
		Path &	result,
		const PathVertex *	vt,
		const PathEdge *	succEdge,
		int	maxInteractions,
		MemoryPool &	pool
	)

static

Create a connection path between two vertices.

This function is conceptually similar to connect(). However, instead of a single edge, it potentially generates an entire connection path, where intermediate vertices are either index-matched medium transitions or other surface scattering events of type BSDF::ENull.

This is important to support efficient direct illumination sampling through such surfaces (e.g. a heterogeneous medium or a leaf with textured alpha transparency).

Parameters

scene	Pointer to the underlying scene
predEdge	Pointer to an edge between `vs` and its predecessor (which is not needed by this function)
vs	First path vertex to be connected.
result	A path data structure that will be filled with the created vertices and edges
vt	Second path vertex to be connected.
succEdge	Pointer to an edge between `vt` and its successor (which is not needed by this function)
maxInteractions	Specifies the maximum permissible number of intermediate vertices (-1 == arbitrarily many)
pool	Reference to memory pool that will be used to allocate edges and vertices.

Returns: true upon success, false when there is no throughput or an inconsistency has been detected.

bool mitsuba::PathEdge::pathConnectAndCollapse	(	const Scene *	scene,
		const PathEdge *	predEdge,
		const PathVertex *	vs,
		const PathVertex *	vt,
		const PathEdge *	succEdge,
		int &	interactions
	)

Create a connection path between two vertices and collapse it into a single edge that summarizes its properties.

This function can be thought of as being half-way in between connect() and pathConnect(). Like pathConnect(), it potentially generates an entire connection path between the specified endpoints, where intermediate vertices are either index-matched medium transitions or other surface scattering events of type BSDF::ENull.

This is important to support efficient direct illumination sampling through such surfaces (e.g. a heterogeneous medium or a leaf with textured alpha transparency).

However, this variant does not return the intermediate vertices and edges – instead, everything is collapsed into a single edge that captures the aggregate weight and probability densities.

This function is used by bidirectional path tracing, since it creates connections through index-matched boundaries but does not require explicit knowledge about the associated path vertices.

Parameters

scene	Pointer to the underlying scene
predEdge	Pointer to an edge between `vs` and its predecessor (which is not needed by this function)
vs	First path vertex to be connected.
vt	Second path vertex to be connected.
succEdge	Pointer to an edge between `vt` and its successor (which is not needed by this function)
interactions	Specifies the maximum permissible number of index-matched medium transitions or BSDF::ENull scattering events on the way to the light source. (`interactions<0` means arbitrarily many). When the function is successful, this parameter will additionally be used to return the actual number of intermediate interactions.

Returns: true upon success, false when there is no throughput or an inconsistency has been detected.

bool mitsuba::PathEdge::perturbDirection	(	const Scene *	scene,
		const PathVertex *	pred,
		const Ray &	ray,
		Float	dist,
		PathVertex::EVertexType	desiredType,
		PathVertex *	next,
		ETransportMode	mode
	)

Create a perturbed successor vertex and edge.

This function behaves similar to sampleNext() in that it generates a successor edge and vertex.

The main difference is that the desired direction, distance, and type of the successor vertex are all specified, which makes the sampling process completely deterministic. This is useful for implementing path-space perturbation strategies.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the preceding vertex
ray	Specifies the direction and origin associated with one endpoint of the edge. The sampling routine will then determine the other endpoint.
dist	Specifies the desired distance between the current vertex and `succ` (this only applies when `desiredType=EMediumInteraction`)
desiredType	Specifies the desired vertex type of `succ`.
succ	Pointer to an unused vertex data structure, which will be filled with information about the successor vertex
mode	Specifies whether radiance or importance is being transported

Returns: true on success

bool mitsuba::PathEdge::sampleNext	(	const Scene *	scene,
		Sampler *	sampler,
		const PathVertex *	pred,
		const Ray &	ray,
		PathVertex *	next,
		ETransportMode	mode
	)

Given a ray ray, sample a distance in this direction and fill the edge data structure, as well as its target vertex with content.

Parameters

scene	Pointer to the underlying scene
sampler	Pointer to a sample generator
pred	Pointer to the preceding vertex
ray	Specifies the direction and origin associated with one endpoint of the edge. The sampling routine will then determine the other endpoint.
succ	Pointer to an unused vertex data structure, which will be filled with information about the successor vertex
mode	Specifies whether radiance or importance is being transported

Returns: true on success

std::string mitsuba::PathEdge::toString ( ) const

Return a string representation of the information stored in this vertex.

bool mitsuba::PathEdge::verify	(	const Scene *	scene,
		const PathVertex *	adjL,
		const PathVertex *	adjE,
		ETransportMode	mode,
		std::ostream &	os
	)		const

Verify the cached values stored in this path vertex for consistency.

This function re-evaluates a series of quantities associated with this edge and compares them to locally cached values. If any mismatch is found, the function sends debug output to a specified output stream and returns false.

Parameters

scene	Pointer to the underlying scene
pred	Pointer to the vertex adjacent in the emitter direction or `NULL`
succ	Pointer to the vertex adjacent in the sensor direction or `NULL`
mode	Transport mode – disambiguates the meaning of `pred` and `succ`.
os	Target output stream for error messages

Member Data Documentation

Vector mitsuba::PathEdge::d

Normalized direction vector associated with this edge.

The direction always points along the light path (from the light)

Float mitsuba::PathEdge::length

Length of this edge in world-space distance units.

Note that edges adjacent to supernodes have length zero to mark them as such.

const Medium* mitsuba::PathEdge::medium

Pointer to the medium that contains this edge (where NULL is vacuum)

Float mitsuba::PathEdge::pdf[ETransportModes]

Medium sampling density of the adjacent vertices.

This field stores the probability of sampling the preceding and successive path vertices using the sampling technique implemented by the function PathEdge::sampleNext(). Depending on whether or not they are medium interactions, this eintries either store a density per unit length or a discrete probability.

Spectrum mitsuba::PathEdge::weight[ETransportModes]

Measurement contribution weight.

This field stores the terms of the path-space measurement contribution function that are coupled to this specific edge divided by the associated density function.

More specifically, it stores the transmittance of the medium across this edge divided by the density per unit length of the adjacent vertices int the radiance and importance transport directions (hence, it is an array with two entries).

Note that this field only accounts for medium-related terms. The interactions with vertices are captured by PathVertex::weight.

The documentation for this struct was generated from the following file:

include/mitsuba/bidir/edge.h

Public Member Functions

Public Attributes

Query functions

Miscellaneous

Detailed Description

Member Enumeration Documentation

Member Function Documentation

Member Data Documentation